Synthesis, characterization and crystal structures of some tungsten and triosmium carbonyl complexes with monopyridyl and dipyridyl azo ligands

Substitution reactions of [W(CO)5(THF)] with the azo-functionalized monopyridyl and dipyridyl ligands, namely, 4-phenylazopyridine L1 and 4,4′-azopyridine L2, readily afford two tungsten carbonyl complexes [W(CO)5(NC5H4NNC6H5)] (1) and [(CO)5W(μ-NC5H4NNC5H4N)W(CO)5] (2) in good yields. Ligation of L1 and L2 with the activated triosmium carbonyl cluster [Os3(CO)10(NCMe)2] by ortho-metallation reaction provides [Os3(μ-H)(CO)10(μ-NC5H3NNC6H5)] (3) and the linking cluster [Os3(μ-H)(CO)10(μ-NC5H3NNC5H3N)Os3(μ-H)(CO)10] (4) in satisfactory yields. All of the complexes have been fully characterized by IR, 1H-NMR, UV–vis spectroscopies, fast atom bombardment (FAB) mass spectrometry and electrochemical measurements. The solid-state molecular structures of 1–4 have been ascertained by single-crystal X-ray diffraction methods. The structures of 1 and 3 involve the coordination of L1 to one {W(CO)5} and {Os3(CO)10} moieties, respectively. In the case of 2 and 4, two identical metal cores are linked together by the bridging ligand L2. Spectroscopic investigations revealed that the metal-to-ligand charge transfer (MLCT) transitions of 1 and 2 demonstrate strong solvent dependency, displaying a large negative solvatochromism in a wide range of organic solvents.